Antarctica's buried lakes are connected by a network of rivers moving water far beneath the surface, say UK scientists.

It was thought the sub-glacial lakes had been completely sealed for millions of years, enabling unique species to evolve in them.

Writing in the journal Nature, experts say international plans to drill into the lakes may now have to be reviewed.

Any attempts to drill into one body of water risks contaminating others.

"What this paper shows is that not only could you contaminate a lake, you could contaminate the whole drainage system," lead author Duncan Wingham, of University College London, told the BBC News website.

Time capsules

The sub-glacial lakes of Antarctica are regarded as "time capsules" of the period when the continent began to freeze over.

Vostok formed around 16 million years ago

Scientists believe any life they contain might shed light on extreme environments on other worlds, such as the ice-bound ocean on Jupiter's moon Europa.

The presence of the drainage system may change current thinking on the chances of finding microbial life that has evolved "independently".

"The notion that these things have been sitting in the lakes evolving for millions of years probably won't wash," said Professor Wingham.

"I think the idea that they have an isolated biological environment where things have gone their own way will have to be re-examined."

Professor Martin Siegert, of the University of Bristol, a co-author of the Nature study, said there would still be a very interesting microbiological story to uncover.

"We have always thought of sub-glacial lakes as being distinct bodies isolated from each other," he said.

"For at least some of these lakes, that won't be true but they will still be isolated from the atmosphere."

Time capsules

It was once thought the Antarctic continent was too cold for water to exist in liquid form beneath its frozen wastes.

LAKE VOSTOK - ANTARCTICA

There are more than 150 sub-glacial lakes in Antarctica; Vostok is the biggest

At 14,000 sq km, it is about the extent of Lake Ontario and is up to 500m deep in places.

Overlying ice layers reveal a 400,000-year environmental record with microbes present throughout the core

Many scientists consider Vostok to be a good model for the ecosystems that might exist on Jupiter's frozen moons

But since the 1960s, satellites and aircraft with powerful radar devices have discovered more and more lakes buried kilometres beneath the thick ice sheet.

More than 150 have been detected so far, but they are expected to run into thousands.

The largest underground body of water in Antarctica is known as Lake Vostok, which is 250km (155 miles) long, 40km (25 miles) wide and 400m (1,300ft) deep.

The US space agency (Nasa) and the Russian academy of sciences are planning to break through the ice to sample the water for life.

There are also proposals to explore and sample Lake Ellsworth in west Antarctica by a team involving 14 UK universities and research institutions, plus scientists from Chile, the US, Sweden, Belgium, Germany and New Zealand.

Cynan Ellis-Evans of the British Antarctic Survey in Cambridge, UK, said the idea of using a small lake away from Vostok to test methods would now have to be looked at again.

"This paper indicates that lakes may well be connected at irregular time intervals and that even an apparently isolated lake can breach and transfer water hundreds of kilometres to other distant lakes so the contamination potential in relation to small lakes is greater than we'd previously thought," he said.

But he said evidence from examining shorelines suggested larger lakes like Vostok were relatively stable.

"I am of the view that Vostok and other similar large lakes have developed in isolation and so the interest from a biological viewpoint will remain high."

Satellite data

The latest research was carried out by scientists at the Natural Environment Research Council (Nerc) Centre for Polar Observation and Modelling (CPOM) at UCL, the University of Bristol and University of Cambridge.

They took ultra-precise measurements of a region in East Antarctica - home to some of the oldest, thickest ice on the continent - using radars on the European Space Agency's ERS-2 satellite.

The satellite found synchronous changes in the surface height at several locations hundreds of kilometres apart.